Eukaryotic Viruses Taxonomy characters: nucleic acid type; enveloped or naked; capsid shape; assembly site in host (nucleus or cytoplasm)

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Presentation transcript:

Eukaryotic Viruses Taxonomy characters: nucleic acid type; enveloped or naked; capsid shape; assembly site in host (nucleus or cytoplasm)

Attachment and Penetration: Attachment phase is conceptually similar to phage. Penetration can be very different (capsid may enter).

Enveloped virus fusing with endosome membrane for release of capsid. NOTE: in both mechanisms the nucleic acid is “uncoated”, i.e. capsid disassembles.

DNA virus Papovavirus (warts) Transcription & replication in nucleus; capsid assembly in nucleus. Release by exocytosis

RNA Virus Types Polio; common cold (RdRp) In the cytoplasm. In the cytoplasm; except influenza

Orthomyxoviruses (Influenza Virus): Attachment and penetration by endocytosis, then -ssRNA is uncoated. Unique for RNA viruses to replicate in the nucleus; Uses RdRp to make +ssRNA then to –ssRNA. Needs a capped primer (C) for mRNA synthesis and ribosome recognition; steals C from host mRNA at 5’end. Viral envelope proteins transported from RER to GA to plasma membrane; others associate with –ssRNA to form nucleocapsid. Budding release (below):

RNA viruses = respiratory enteric orphan viruses In the cytoplasm.

Retrovirus (+RNA)

Infection Types and Outcomes Acute versus Persistent Infections: –Chronic (replicates at low levels & constant yet mild symptoms) –Latent (stops reproduction after initial infection; goes dormant until induced to activate replication again) –Slow (vary slow replication and spread; years before symptoms) Cytocidal effects (death) and cell damage: –Inhibit host macromolecule synthesis –Lysosome malfunction (host cell self digests) –Plasma membrane abnormalities –Direct viral protein toxicity –Protein aggregation (inclusion bodies) –Host cell changes to a malignant cell (cancer) Tumors form by neoplasia and anaplasa; may spread by metastasis. Virus may carry oncogenes (genes for various cancer causing protein). Viral promotors may insert and turn on expression of host oncogenes. 8 cancers involving viruses: Burkitt’s lymphoma and nasopharyngeal carcinoma (Epstein-Barr virus); cervical cancer (papillomavirus); Kaposi’s sarcoma (herpes 8), Hepatitis B & C, T-cell and hairy-cell leukemias, Rous sarcoma.